Really you MUST check out the Makita LXT series BEFORE you buy anything else.
They are extremely well designed and built, LIGHTER, but more powerful then any other similar voltage cordless unit. I use their 18 volt series and it has never let me down. The impact driver leaves all other drivers I have ever used in the dust in terms of power and ease of operation--as I get older, I prefer my tools to be lighter as well as powerful.
Just a note, when I first bought the set, I laughed at the inclusion of their LCD light on eact tool that helps to light up the area of operation, but NOW I laugh at myself each time it turns on automatically when I pull the trigger, because more often then not I need more light to see what I am doing, and the little LCD actaully throws enought light for me to be grateful for it. !!
Just my 2 cents-- they are AWESOME!!